1. Field of the Invention
The present invention relates to a CDMA (Code Division Multiple Access) transmitter-receiver capable of varying a transmission rate.
2. Description of the Background Art
A CDMA communication system must minimize transmission power per channel to increase its capacity in terms of the number of subscribers because they communicate using the same frequency band.
A conventional CDMA system like that recommended in the United States (IS-95) varies the transmission rate per channel by applying to voice encoding a block coding scheme that varies the bit rate of the voice encoding, and controls the transmission power in accordance with the transmission rate.
Such a conventional CDMA system has a drawback of being inapplicable to the voice encoding without using the block coding such as PCM (Pulse Code Modulation) and ADPCM (Adaptive Differential PCM). In addition, the block coding of the conventional CDMA system requires very complicated coding and decoding.